SHEAR-INDUCED OPENING OF THE CORONAL MAGNETIC-FIELD

This work describes the evolution of a model solar corona in response to motions of the footpoints of its magnetic field. The mathematics in volved is semianalytic, with the only numerical solution being that of an ordinary differential equation. This approach, while lacking the f lexibility and physical details of full MHD simulations, allows for ve ry rapid computation along with complete and rigorous exploration of t he model's implications. We find that the model coronal field bulges u pward, at first slowly and then more dramatically, in response to foot point displacements. The energy in the field rises monotonically from that of the initial potential state, and the field configuration and e nergy approach asymptotically that of a fully open held. Concurrently, electric currents develop and concentrate into a current sheet as the limiting case of the open field is approached. Examination of the equ ations show rigorously that in the asymptotic limit of the fully open field, the current layer becomes a true ideal MHD singularity